From U.S. Pat. No. 4,594,984, a control system is known in which a control device with constant control action is arranged for controlling in the lean region (preferably around lambda=1.2). Since the probe output signal has a relatively small increase in this region, a greater control accuracy is achieved with the continuous-action control device than with the usual two-position control. In the above U.S. Pat. Pat. application, it is also stated that this continuous-action control device cannot be used for a lambda=1 control, since the lambda probe has a steep voltage jump at lambda=1 and, as a result, the control device would always be at the lean or rich limit.
U.S. Pat. No. 4,601,276 discloses a method and apparatus for controlling the air/fuel mixture of an internal combustion engine by means of oxygen probes. The probes are mounted in respective combustion chambers of the engine. This arrangement affords the advantage that the direct measurement of the result of combustion makes possible a very rapid response of the control. The duration of detection of the components of the air/fuel mixture metered to the engine can be considerably reduced. In addition, extreme conditions such as too rich or too lean can be detected after a few cycles of the particular cylinder in question and an appropriate response can be made. The entire engine can be monitored and the measuring results from cylinder to cylinder can be evaluated serially in the ignition sequence. In addition to this, the invention of U.S. Pat. No. 4,601,276 permits the simultaneous monitoring of each individual cylinder. This affords the advantage that variations from cylinder to cylidner in the composition of the mixture can be eliminated. Signals of oxygen probes which are mounted directly in the combustion chambers of an engine can be evaluated for the method and apparatus of U.S. Pat. No. 4,601,276. For this reason, evaluation of the probe signals is undertaken differently than with an oxygen probe mounted in the exhaust of an internal combustion engine, that is, the oxygen probe is continuously subjected to exhaust gases during operation of the engine.
Furthermore, the method and apparatus of U.S. Pat. No. 4,601,276 requires that several oxygen probes also be used in an internal combustion engine having several cylinders and this leads to considerable increased expense.
The invention is based on the object to improve a control system for controlling the air/fuel ratio in an internal combustion engine by means of an oxygen probe mounted in the exhaust system with the oxygen probe being continuously subjected to the exhaust gas of the engine. The control system is improved in with respect to reducing the overall emission of the main pollutant components.